The present invention relates to a method for knock control in an internal combustion engine.
Carrying out a so-called knock control in internal combustion engines is known in the art. In so doing, a combustion process in the cylinders of the internal combustion engine is monitored for knocking combustion. Knocking combustion is identified by characteristic vibrations that may be detected using so-called knock sensors which are mounted on the housing of the internal combustion engine. Knocking combustion is, for example, a function of the quality of a fuel being used, the compression of the fuel/air mixture in the cylinders and/or the moment of ignition. The ignition timing is retarded by a specifiable amount as a function of the detected knocking combustion. Since retarding the ignition timing leads to loss of torque and increased fuel consumption, running the internal combustion engine as close as possible to a so-called knock limit is known in the art. The knock control in this case runs the internal combustion engine as close as possible to the knock limit. Here, the ignition timing is controlled according to the actual signals determined by the knock sensors.
Detecting knock using knock sensors, which are typically designed as structure-borne noise sensors, is known in the art. The use of ionic current sensors or pressure sensors is also conceivable. At least one cylinder of the internal combustion engine is assigned to each of these knock sensors. The control unit has two evaluation electronics to which the sensors are assigned, and by which the sensor signals are evaluated in a cylinder-specific manner. The evaluation circuit supplies the result of the preprocessed sensor signals to a control electronics, which typically is integrated within an engine control unit. Here, knocking of the individual cylinders is detected, and the ignition angle retard and moment of ignition are calculated.
During normal use of the knock control, the evaluation electronics are continually monitored for correct functioning by a diagnostic. If a malfunction is determined, the system automatically switches to safety knock control to prevent damage to the internal combustion engine. This safety knock control provides that of a safety retard of the ignition timing is implemented for all cylinders of the internal combustion engine. However, in this context, it is disadvantageous that whenever the moment of ignition, and thus the ignition angle, is retarded away from the optimal ignition angle, the efficiency and the power output of the internal combustion engine are reduced, thereby increasing fuel consumption. In turbo-charged internal combustion engines, retarding the moment of ignition may cause the charging-air pressure to drop, which can lead to power losses of up to 40%.
The method according to the present invention offers the following advantage: in the event of a failure or malfunction of an evaluation electronics of the knock control, a safety retard of the moments of ignition is not necessary for all cylinders of the internal combustion engine. Since, upon detecting a malfunction of at least one of the evaluation electronics, the at least one cylinder assigned to this evaluation electronics is linked to the control of at least one cylinder with intact evaluation electronics, all cylinders of the internal combustion engine are advantageously not automatically switched to the maximum safety retard, but rather the at least one cylinder to which the malfunctioning evaluation electronics circuit is assigned is guided by another cylinder of the internal combustion engine whose evaluation electronics is in working order. This ensures that the cylinders with operational evaluation electronics may still be operated using an optimal moment of ignition, while only the at least one cylinder with malfunctioning evaluation electronics is operated with retarded ignition timing which, however, is below the previously known safety ignition retard. The overall result is that the efficiency of the internal combustion engine is only insignificantly impaired. In particular, this guidance of the cylinder having defective evaluation electronics makes it possible to operate the cylinder close to its knock limit even if its evaluation electronics malfunction.
If an evaluation electronics circuit fails, a guide cylinder function is activated for the cylinders assigned to this evaluation electronics. This means that the cylinders of the defective evaluation electronics are guided by cylinders of an intact evaluation electronics. The central control electronics (engine control unit) detects knocking, chooses which cylinders assume guidance of the cylinder assigned to the failed evaluation electronics, and calculates the resulting ignition retard. Only if all evaluation electronics are detected as defective is a uniform safety ignition retard activated for all cylinders.
For the guide cylinder function, at least one cylinder of an intact evaluation electronics is selected as the guide cylinder. The ignition angle settings of the at least one guided cylinder are derived from those of the at least one guide cylinder. This preferably results in several possibilities. Thus, an ignition angle setting of the guided cylinder may be the same as the ignition angle of the guide cylinder. Furthermore, it is preferred if the ignition angle setting of at the least one guided cylinder corresponds to an ignition angle setting of the at least one guide cylinder plus a safety offset (timing retard away from the knock limit).
Another preferred embodiment of the present invention provides that the retard of the ignition angle for the at least one guided cylinder is made in one step following a knock event at the guide cylinder. Furthermore, it is preferred if the retard for the at least one guided cylinder is effected in several small steps following a knock event in the at least one guide cylinder.
Finally, it is preferable if the cylinder which uses the greatest retard of the ignition timing is established as the guide cylinder. Finally, it is also preferred if, during initialization of the control electronics and the evaluation electronics, respectively, it is determined which cylinders may be used as the guide cylinder in the particular groups assigned to an evaluation electronics.